(1) Field of the Invention
The present invention relates to a method of assisted piloting for a rotary wing aircraft that has at least one propulsion propeller, and also to an assisted piloting device and to an aircraft.
(2) Description of Related Art
Aircraft include in particular rotorcraft, i.e. aircraft that have a rotary wing. Furthermore, certain rotorcraft are also provided with an additional propulsion unit.
A rotary wing aircraft having an additional propulsion unit, which propulsion unit has at least one propulsion propeller, is referred to for convenience below as a “hybrid aircraft”.
Such a hybrid aircraft may comprise:
thrust control means for controlling the thrust generated by the propulsion unit;
collective control means for controlling the collective pitch of the blades of the rotary wing; and
cyclic control means for controlling the cyclic pitch of the blades of the rotary wing.
Under such circumstances, it can be seen that the flight controls are redundant.
In order to control longitudinal acceleration of a hybrid aircraft, a pilot may use the thrust control means, and/or may act on the cyclic control means as in a conventional helicopter.
Likewise, in order to control vertical acceleration of a hybrid aircraft in order to control climbing or descent of the hybrid aircraft, a pilot can act, as in a conventional helicopter, on the collective control means without changing the attitude of the hybrid aircraft, and/or can, for example, both change the longitudinal attitude of the aircraft with the help of the cyclic control means and also make use of the thrust control means.
It can be understood that a multitude of control combinations can be envisaged for piloting a hybrid aircraft.
It can thus be useful to provide a method and a device for lightening the workload on the pilot by assisting the pilot when performing maneuvers by controlling the rotary wing and the propulsion unit.
It may be observed that the state of the art includes US patent document 2008/0237392 published on Oct. 2, 2008. That US patent document 2008/0237392 describes an aircraft having a rotary wing, a fixed wing, and a propulsion propeller.
A control system of the aircraft enables a person to select a control technique for achieving an operational objective.
More precisely, in its paragraphs 63 to 71, document US 2008/0237392 describes a vertical and longitudinal control module of the aircraft that receives input data relating to commands for changing a pitching angle and a vertical speed.
That input data is filtered and then subjected to processing before being transmitted to an inversion module, the inversion module determining the changes to be applied to the control means of the aircraft.
Furthermore, it should be observed that in paragraphs 72 to 75 of that document, a longitudinal acceleration order is processed by a limiter in order to transform it into a limited order (referred to as a “constrained acceleration”) seeking to comply with the limits of the engines.
That limited order is integrated and then compared with the speed of the aircraft in order to generate an error signal. After processing, the error signal gives rise to a setpoint speed referred to as a “forward speed pseudo-control”. The changes to the rotary wing in pitch, and the changes to the propellers are derived from that parameter.
It should also be observed that an acceleration and a load factor represent two concepts that are substantially different.